Volumetric solar receiver

ABSTRACT

A volumetric receiver vessel for heating a fluid with concentrated solar radiation which includes: an external housing having an aperture at the front end; an internal housing separating fluid entering the vessel from fluid exiting thereof; a window covering the aperture of the vessel, where the window closes and seals the aperture of said vessel against a non-metallic seal; and a radiation absorber, located inside the vessel and places to absorb radiation entering the vessel through said window on a radiation absorbing surface, where said surface include at least two zones with different radiation absorption coefficients.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119

to U.S. Provisional Patent Application Ser. No. 61/577,028, filed Dec.18, 2011, and entitled “The Klein solar thermal receiver”; which isincorporated herein by reference in its entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates generally to a system using concentratedradiation as the mode of heating a fluid situated inside the vessel, andmore particularly solar energy systems with solar receivers.

BACKGROUND OF THE INVENTION

The following publications, the disclosures of which are herebyincorporated by reference, are believed to represent the current stateof the art:

U.S. Pat. Nos. 5,931,158; 5,947,114; 6,516,792 B2,

-   Kribus, A., Zaibel, R., Carey, D. Segal, A., Karni, J. 1998, “A    solar-driven combined cycle power plant”, Solar Energy    62(2):121-129.-   Mills, D., 2004, “Advances in solar thermal electricity technology”,    Solar Energy 76:19-31.-   Woerner, A., and Tamme, R., 1998, “CO₂ reforming of methane in a    solar driven volumetric receiver-reactor” Catalysis Today    46:165-174.-   Berman, A., Karn, R. K., Epstein, M., 2005, “Kinetics of steam    reforming of methane on Ru/Al₂0₃ catalysts promoted with Mn oxides”.    Applied catalysis A: General 282:73-83.-   Gordon, J. M. and Ries, H, 1993 “Tailored edge-ray concentrators as    ideal second stages for Fresnel reflectors”, Applied Optics    32(13):2243-2250

The invention relates to radiation based energy systems, such as systemsusing concentrated solar radiation to produce heat, electricity or todrive chemical reactions. The concentrated solar radiation can be usedto directly or indirectly, drive turbines for electricity production.Central to the energy system is the vessel converting the radiation tosensible heat. This vessel is often called a solar receiver.

The invention relates to a kind of solar receiver commonly called avolumetric receiver. In this type of vessel, the working fluid enteringthe receiver, for the purpose of heating and possibly also for chemicalconversion of the fluid, is directly exposed to concentrated solarradiation by allowing the radiation to enter the vessel through awindow. The window prevents the working fluid from mixing with ambientair, and prevents loss of pressure and/or the loss of already acquiredheat in the incoming fluid.

One of the most challenging aspects of this type of vessel ismaintaining the integrity of the window. Pressure stresses, thermalstresses and issues of differences of thermal expansion between thewindow and other material in direct contact with the window can causethe window to crack, break or shatter. It is an object of the presentinvention to provide a positioning and sealing mechanism for the windowthat will put the least stress on the window and a design for aradiation absorber that will contribute to the lowering of thermalstresses on the window.

Another challenging aspect of this type of receiver is the integrity ofthe radiation absorber. Pressure stresses and thermal stresses andissues of differences of thermal expansion between the absorber andother material in direct contact with the absorber can cause theabsorber to melt, crack, break, crumble or shatter. It is an object ofthe present invention to provide a solution for, this problem byapplying different materials with different radiation absorbingproperties in different parts of the absorber.

SUMMARY OF THE INVENTION

The present invention seeks to provide improved vessels for heating afluid with concentrated, radiation, preferably solar radiation.

There is thus provided in accordance with a preferred embodiment of thepresent invention a vessel for heating a fluid with concentratedradiation, which includes: a housing with an aperture and an ingress andan egress for fluid; a window covering the aperture in said housing foradmitting and passing into the vessel concentrated radiation; a flowguide separating the fluid from the ingress from the fluid from theegress; and a permeable radiation absorber.

Preferably, the window is flat.

Most preferably the window covering the aperture is concave with thecenter of the window being deeper inside the body of the radiationreceiving vessel than the rim of said window. The concave shapepreferably follows an axis symmetric shape such as the radius of asphere, a parabola, cone, capped cone, a combination of the mentionedshapes and other concave possibilities.

Preferably, the window is placed on a seal to seal the aperture fromfluid exchange with the ambient air.

Most preferably the window is kept in place on the seal in the absenceof any mechanism other than weight, gravity and friction to keep it inplace. No other material is in direct contact with the window than theseal.

Preferably, the window flange is actively cooled.

Preferably, the window is actively cooled.

Most preferably, the window is actively cooled from the outside.

Preferably, the radiation absorber has at least two different areas withdifferent radiation absorptivity, accomplished by the use of differentabsorption materials or by applying different external coating on theradiation absorbing side of the radiation absorber.

There is also provided in accordance with a different preferredembodiment of the present invention a system for heating fluid withconcentrated, radiation, preferably solar radiation. The systemincludes: concentrating devices to concentrate radiation from aradiation source; a vessel in which the concentrated radiation heats afluid and a utilizer of the stored energy in the fluid.

Preferably, the fluid contains any, all or a subset of the compounds;oxygen, methane, hydrogen, carbon dioxide, carbon monoxide, nitrogen,H₂O.

Most preferably, the fluid is air.

Preferably, the radiation is concentrated and directed to the radiationreceiving vessel by a primary optical device such as; an optical lens, aheliostat field with mirrors directing solar radiation to a target or aparabolic mirror or any combination of these concepts.

Preferably, the radiation from the primary optical device is furtherconcentrated by a secondary optical device located in close proximity infront of or around the aperture of the radiation receiving vessel suchas; additional lens or lenses, a compound parabolic concentrator, aconcentrator following closely or approximately the mathematical shapeof a truncated cone, tailor-edge-ray concentrator and a trumpetflow-line concentrator.

Preferably, the secondary optical device is actively cooled by water orother liquid coolant.

Preferably, the radiation receiving vessel is configured as described inparagraph [0015] to [0023] in the present description, to heat a fluidby incoming concentrated radiation.

Preferably, the heated fluid is utilized to heat, directly orindirectly, all or part of the fluid to drive a turbine for electricalgeneration.

Most preferably, the heated fluid is used to heat all or part of thefluid, directly or indirectly, to drive a gas turbine for electricalgeneration.

Preferably, the heated fluid from the radiation receiving vessel, whichdoes not have a sufficiently high temperature to, economically orpractically, be applied to electricity generation can be used forheating purposes such as; heat pump, boiler, absorption chiller, hotwater heater, space heater.

Most preferably, the fluid from the radiation absorbing vessel is firstused to drive a turbine for electrical generation and afterwards usedfor heating purposes as described in [0033].

There is also provided in accordance with a different preferredembodiment of the present invention a system for heating fluid withconcentrated, radiation, preferably solar radiation and to providesufficient heat to also chemically alter the composition of the fluid.The system includes: concentrating devices to concentrate radiation froma radiation source and funnel the concentrated radiation to a reactionvessel; a reaction vessel receiving the concentrated radiation to heatand chemically alter a fluid and a utilizer of the stored heat andchemical compounds in the fluid.

Preferably, the incoming fluid to the reaction vessel contains any, allor a subset of the compounds; oxygen, methane, hydrogen, carbon dioxide,carbon monoxide, nitrogen, H₂O.

Preferably, the outgoing fluid from the reaction vessel contains any,all or a subset of the compounds; oxygen, methane, hydrogen, carbondioxide, carbon monoxide, nitrogen, H₂O.

Preferably, the radiation is concentrated and directed to the radiationreceiving vessel by a primary optical device such as; an optical lens, aheliostat field with mirrors directing solar radiation to a target or aparabolic mirror or any combination of these concepts.

Preferably, the radiation from the primary optical device is furtherconcentrated by a secondary optical device located in close proximity infront of or around the aperture of the radiation receiving vessel suchas; additional lens or lenses, compound parabolic concentrator, aconcentrator following closely or approximately the mathematical shapeof a truncated cone, tailor-edge-ray concentrator and a trumpetflow-line concentrator.

Preferably, the secondary optical device is actively cooled by water orother liquid coolant.

Preferably, a reaction vessel for heating and chemically altering afluid with concentrated, radiation, preferably solar radiation, is used.

Preferably, this reaction vessel is a vessel, which includes; a housingwith an ingress and an egress for fluid and an aperture, a windowcovering the aperture of the housing for admitting and passing into thevessel concentrated radiation, a flow guide separating the fluid fromthe ingress from the fluid from the egress, a permeable radiationabsorber.

Preferably, the window in the reaction vessel described in [0042] isflat.

Most preferably the window covering the aperture of the reaction vesseldescribed in [0042] is concave with the center of the window beingdeeper inside the body of the radiation receiving vessel than the rim ofsaid window. The concave shape preferably follows an axis symmetricshape such as the radius of a sphere, a parabola, cone, capped cone, acombination of the mentioned shapes and other concave possibilities.

Preferably, the window is placed on a seal to seal the aperture thereaction vessel described in [0042] from fluid exchange with theambient.

Most preferably the window of the reaction vessel described in [0042] iskept in place on the seal in the absence of any mechanism other thanweight, gravity and friction to keep it in place.

Preferably, the window flange of the reaction vessel described in [0042]is actively cooled.

Preferably, the window of the reaction vessel described in [0042] isactively cooled.

Most preferably, the window of the reaction vessel described in [0042]is actively cooled from the outside.

Preferably, the radiation absorber of the reaction vessel described in[0042] is able to absorb the concentrated radiation and transfer theheat to the fluid.

Most preferably, the radiation absorber of the reaction vessel describedin [0042] has at least two different areas with different radiationabsorptivity, ascertained by the use of different absorption materialsor by applying different external coating on the radiation absorbingside of the radiation absorber.

Preferably, the reaction vessel described in [0042] is equipped with ahigh surface area covered with catalyst material to enable chemicalalterations of the fluid inside the vessel.

Most preferably, the high surface area provided with catalyst materialis integrated with the radiation absorbing surface.

Preferably, the heated fluid exiting the reaction vessel described in[0042] is used to preheat the fluid entering the reaction vesseldescribed in [0042].

Preferably, the fluid leaving the reaction vessel is used to performchemical reactions such as; combustion of the fluid and conversion ofthe fluid to liquid fuel.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a simplified partially block diagram, partially schematicillustration of a system for heating a fluid with concentrated radiationin a vessel, constructed and operative in accordance with a preferredembodiment of the present invention; and

FIG. 2 is an enlarged view of area A of the vessel shown in FIG. 1.

FIG. 3 is a schematic view of the radiation absorbing surface, 127,shown in FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1, which is a schematic illustration of avessel for heating a fluid with concentrated solar radiation,constructed and operative in accordance with a preferred embodiment ofthe present invention.

As seen in FIG. 1, the present invention provides a system 100 forheating a fluid with concentrated radiation including a fluid supplysource 102. Examples of fluids include: oxygen, nitrogen, carbondioxide, carbon monoxide, hydrogen, gaseous hydrocarbons, steam or acombination of the above mentioned fluids.

A radiation receiving vessel 120, such as a vessel described inter aliain the above-referenced US patents: U.S. Pat. No. 5,931,158, U.S. Pat.No. 5,947,114 and U.S. Pat. No. 6,516,792 B2, the disclosures of whichare hereby incorporated by reference, receives the fluid from the fluidsupply source 102, preferably at a pressure of between 1-200 bar, andmost preferably at a pressure of about 1.5-10 bars.

Preferably, radiation is highly concentrated prior to impinging on theradiation receiving vessel 120.

Preferably, the highly concentrated radiation originates from the sun.

Preferably, concentration of the solar radiation is provided bydirecting incoming solar radiation through a concentrator 125.Concentrator 125 may have various possible configurations such as thosedescribed inter alia in the above-referenced publications of Kribus, A.,Zaibel, R., Carey, D. Segal, A., Karni, J. 1998, “A solar-drivencombined cycle power plant”, Solar Energy 62(2):121-129, and Mills, D.,2004, “Advances in solar thermal electricity technology”, Solar Energy76:19-31, the disclosures of which are hereby incorporated by reference.Heliostat fields and parabolic dished are the most preferred primaryconcentrators for concentrator 125. The concentrator 125 can, but is notforced to, consist of both primary and secondary optics, example ofwhich are described inter alia in the above-referenced publications ofGordon, J. M. and Ries, H, 1993 “Tailored edge-ray concentrators asideal second stages for Fresnel reflectors”, Applied Optics32(13):2243-2250, the disclosures of which are hereby incorporated byreference. Compound parabolic concentrators and cone shapedconcentrators are most preferred as practical secondary optics devicesfor concentrator 125. The output of concentrator 125 is directed througha window 126 of the radiation receiving vessel 120 so as to impinge ontoa radiation absorbing surface 127, located on the permeable heattransfer wall 128. Window 126 is preferably formed of quartz and may beof any suitable shape such as flat or curved. Solar reactors havingconcave windows, described in the above-referenced U.S. patents: U.S.Pat. No. 5,931,158, and U.S. Pat. No. 6,516,794 may be suitable for thispurpose. As used herein, in specifications or in claims, the term“concave” incorporates all shapes, where the center of the shape isdeeper inside vessel 120 than the perimeter of the same shape.

Preferably, window 126 is placed on a seal 140, as illustrated in FIG.2, window 126 is kept in place on seal 140, placed on aperture openingsurface 142, solely by the force of gravity acting on the weight of thewindow 126 and the friction between window 126, the seal 140 and theaperture opening surface 142. Preferably, the window is only in directcontact with the seal and with no other device. If the vessel isoperating under pressure the pressure inside the vessel assists infixing the window in location and to seal the aperture 144, by forcingthe window 126 towards the aperture opening surface 142. Thermalstresses and difference in thermal expansion between the window and itsholding devices have been known in prior art to cause breakage towindows in similar vessels.

The permeable heat transfer wall 128 is preferably formed of siliconcarbide, silicon nitrite, alumina, or metallic wire mesh or othermetallic, high surface area configuration.

The permeable heat transfer wall 128 may employ any suitable catalyst onsurface 127 if the objective of system 100 is not only to heat the fluidfrom the fluid supply source 102, but also to react the fluid. For hightemperature reactions the most preferred catalysts are Ruthenium andRhodium. A somewhat less preferred catalyst is Iridium and even lesspreferred catalysts are Nickel, Platinum and Palladium. These catalystsare preferably applied over a pigmented wash coat which is deposited onhighly porous support structures such as ceramic matrices, preferablyformed of silicon carbide or alumina, as described inter alia in theabove-referenced publications of Woerner, A., and Tamme, R., 1998, “CO₂reforming of methane in a solar driven volumetric receiver-reactor”Catalysis Today 46:165-174, Berman, A., Karn, R. K., Epstein, M., 2005,“Kinetics of steam reforming of methane on Ru/Al₂0₃ catalysts promotedwith Mn oxides”, Applied catalysis A: General 282:73-83, and U.S. Pat.No. 5,431,855, the disclosures of which are hereby incorporated byreference. The permeable heat transfer wall 128 can also be constructedof silicon nitride or on a metallic wire mesh or other metallic, highsurface area configuration and coated with a catalyst appropriate forthe desired reaction. As used herein, in specifications or in claims,the term “silicon carbide” incorporates all compounds, washcoats orother coatings and materials containing any silicon carbide (SiC) orsilicon carbide (SiSiC). As used herein, in specification or in claims,the term “alumina” incorporates all compounds, washcoats or othercoatings and materials containing any alumina (Al₂O₃). As used herein,in specifications or in claims, the term “silicon nitride” incorporatesall compounds, washcoats or other coatings and materials containing anysilicon nitride (Si₃N₄).

The permeable heat transfer wall 128 may consist of several differentmaterials in different axis symmetric zones as illustrated in FIG. 3.The material in each zone is chosen according to the concentration ofradiation expected to impinge thereon. Zone I, illustrated in FIG. 3,may receive the lowest radiation flux and may therefore have the highestradiation absorptivity of the zones. Zone II illustrated in FIG. 3, mayreceive the highest radiation flux and preferably have a low radiationabsorptivity to prevent overheating of the permeable heat transfer wall128 and/or overheating of window 126 as a consequence of a hightemperature of the permeable heat transfer wall 128. Preferably, theshape of zone II is highly concave to prevent reflected radiation fromthe surface 127 on 128 to exit the receiver through window 126. Zone IIwould in such cases be closer to the window in the outer regions than inthe inner/central regions,

The fluid from the fluid supply source 102, supplied to vessel 120 via asupply conduit 121, preferably is caused to impinge on surface 127 ofthe permeable heat transfer wall 128. In a preferred embodiment, conduit121 extends into the reactor 120 and into close proximity with surface127 of the permeable heat transfer wall 128. Alternatively, conduit 121may not necessarily extend into the vessel 120, and fluid from the fluidsupply source 102, supplied to vessel 120 via a supply conduit 121 maybe caused to impinge on surface 127 of permeable heat transfer wall 128by another suitable method.

In accordance with a preferred embodiment of the present invention,window 126 can be cooled, as by a flow of cooling fluid, such aspressurized air from a nozzle 130 impinging on the outside surface 132of window 126. The cooling action prevents excessive heating of thewindow from radiation absorption inside the window. The cooling ofwindow 126 additionally prevents or reduces condensation on an insidesurface 134 of window 126 and resultant reduction in the transparencythereof to incoming solar radiation and consequent excessive heating ofthe window 126.

It will be appreciated by persons skilled in the art that the presentinvention is not limited by what has been particularly shown anddescribed hereinabove. Rather the scope of the present inventionincludes both combinations and sub-combinations of various feature ofthe invention and modifications thereof which may occur to personsskilled in the art upon reading the foregoing description and which arenot in the prior art.

1. A vessel comprising: an external housing with a front end and a rear end, and having an aperture at the front end; an internal housing separating fluid entering the vessel from fluid exiting the vessel; a window covering the aperture of the vessel; a radiation absorber, located inside the vessel and placed to absorb radiation entering the vessel through said window on a radiation absorbing surface, said surface comprising at least two zones with different respective radiation absorption coefficients on a side of the absorber facing said window; a fluid ingress and a fluid egress in the external housing to, respectively, inject therein or withdraw therefrom a fluid in a manner enabling fluid interaction with the radiation absorber.
 2. A vessel according to claim 1, wherein said window is flat.
 3. A vessel according to claim 1, wherein said window is conical.
 4. A vessel according to claim 1, wherein said window is concave in relation to said vessel.
 5. A vessel according 1, wherein the radiation absorber includes a coating that produces the difference in radiation absorptivity.
 6. A vessel according to claim 1, wherein the radiation absorptivity of said radiation absorber surface is higher in a perimeter of said absorber than in a center of said absorber.
 7. A vessel according to claim 6, wherein said radiation absorber surface with a lower radiation absorptivity has a larger distance to the window in its inner regions than in the outer regions.
 8. A vessel according to claim 1, wherein said radiation absorber surface is made of silicon carbide in the outer regions of said radiation absorber and said radiation absorber surface is made of alumina in the inner regions of said radiation absorber.
 9. A vessel according to claim 1, wherein said radiation absorber surface is made of silicon nitride in the outer regions of said radiation absorber and said radiation absorber surface is made of alumina in the inner regions of said radiation absorber.
 10. A vessel comprising: an external housing having a front and a rear end, and having an aperture at the front end; an internal housing separating fluid entering the vessel from fluid exiting thereof; a window covering the aperture of the vessel, where said window closes and seals the aperture of said vessel against a non-metallic seal by contact with only a seal; a radiation absorber, located inside the vessel and placed to absorb radiation entering the vessel through said window on a radiation absorbing surface; a fluid ingress and a fluid egress in the external housing to, respectively, inject therein or withdraw therefrom a fluid in a manner enabling fluid interaction with the radiation absorber.
 11. A vessel according to claim 10, wherein said window is flat.
 12. A vessel according to claim 10, wherein said window is concave in relation to said vessel.
 13. A vessel according to claim 10, wherein said radiation absorbing surface is made of silicon carbide.
 14. A vessel according claim 10, wherein said radiation absorbing surface is made of silicon nitride.
 15. A vessel according to claim 10, wherein said radiation absorbing surface is made of alumina.
 16. A vessel according to claim 10, wherein said radiation absorber consists of at least one material with high radiation absorptivity and one material with low radiation absorptivity.
 17. A vessel according to claim 10, wherein the radiation absorptivity of said radiation absorber surface is higher in a perimeter than in a center of said absorber.
 18. A vessel according to claim 10, wherein said radiation absorber surface with a lower radiation absorptivity has a larger distance to the window in its inner regions than in the outer regions.
 19. A vessel according to claim 10, wherein said radiation absorber surface is made of silicon carbide in the outer regions of said radiation absorber and said radiation absorber surface is made of alumina in the inner regions of said radiation absorber.
 20. A vessel according to claim 10, wherein said radiation absorber surface is made of silicon nitride in the outer regions of said radiation absorber and said radiation absorber surface is made of alumina in the inner regions of said radiation absorber. 